The present invention relates to gas turbine engines and in particular to nose cones found on the fan inlet hubs of such engines.
A removable nose cone, sometimes called a spinner is attached to, and rotates with a hub in the centre of the inlet of a gas turbine engine. This nose cone provides an aerodynamic surface covering the hub hardware and directs the inlet airflow smoothly into the hub region of the gas turbine engine fan.
Conventionally the nose cone is attached to the fan hub by a number of circumferentially spaced, axially extending bolts disposed around the base portion of the cone and engaging the fan hub assembly. To provide access to these bolts, for fitting or removing the nose cone, elliptical holes are provided in the nose cone. Alternatively pockets or indentations below the nominal surface of the cone are formed in the nose cone base region. The bolts are fitted within these pockets which are large enough to accommodate the heads of the bolts.
A problem with both of these arrangements is that the airflow into the fan, over the nose cone, is disturbed, in particular in the region surrounding the fan hub at the root portion of the fan blades. In the first arrangement some air flows into the elliptical holes and also the sharp edges of the hole affect and disturb the remainder of the flow of air passing over them. In the second arrangement there are more rounded edges to the pockets than are found with the holes reducing the effect they have on the airflow passing over them. However the pockets are larger than the holes and so they will effect and disturb the flow over a larger area of the nose cone. The airflow will also flow into these pockets producing eddy flows which will again effect the airflow over the nose cone. Engine testing and analysis have shown that disturbances to the airflow over the nose cone reduces the efficiency of the root portions of the fan downstream of the nose cone. This in turn has a significant effect on the overall engine performance.
Additionally the fabrication of a nose cone incorporating pockets is complex and therefore expensive. The pockets within the nose cone, and to a certain extent the holes, increase the stresses within the nose cone requiring that the nose cone has to be made from thicker material. This undesirably increases the weight of the nose cone.
It is therefore desirable to provide an improved nose cone assembly that addresses the above problems, provides an improved less disturbed airflow into the fan and/or offers improvements generally.
According to the present invention there is provided a nose cone assembly for a gas turbine engine comprising a spinner having a generally conical forward portion and a base portion, a flange is upon the base of the base portion of the spinner, mounting fasteners through the flange attach the spinner to a fan hub of the gas turbine engine; wherein there is an extended profile of the forward portion of the spinner, the base portion of the spinner is disposed radially inside an extended profile of the forward portion of the spinner and the flange extends radially outwards from the base portion of spinner; a fairing is arranged to surround and cover the base portion of the spinner when the nose core assembly is fitted to the fan hub, the fairing when assembled having a generally circumferentially and axially smooth continuous outer surface profile of which continues that of the forward portion of the spinner.
Preferably the fairing is frusto-conical.
By virtue of its frusto-conical shape the fairing is self supporting allowing for a simple attachment means to be used to attach the fairing to the spinner and fan hub.
The nose cone assembly may have an axially curved outer profile.
Preferably an upstream end of the fairing is arranged to abut and be supported from the spinner.
Preferably the spinner is provided with a location feature which axially engages an upstream portion of the fairing.
A seal may be provided at the upstream end of the fairing between the upstream end of the fairing and the spinner. The seal may comprise an annular xe2x80x98Oxe2x80x99 ring. Preferably the annular xe2x80x98Oxe2x80x99 ring seal is set within a recess within an abutting surface of the upstream end of the fairing. The seal may comprise an annular ring which has an omega cross section and which is mounted on the spinner.
Preferably the fasteners extend from the fairing in a substantially radially inwardly directed direction to attach the fairing to the spinner and fan hub. Furthermore the fasteners may extend in a direction generally perpendicular to an outer surface of the fairing in the region of the fasteners. The fasteners are preferably flush with an outer surface of the fairing and may comprise counter sunk screws.
At least three mounting brackets are preferably disposed radially inside the fairing attach the fairing to the spinner and fan hub. The brackets are flexible in a radial direction.
The radial flexibility of the brackets which attach the fairings to the spinner and fan hub allows for and accommodates dimensional mismatches between the fairing, spinner and fan hub.
Preferably the brackets axially locate the fairing.
The brackets may be generally L shaped. They may also be attached using the same mounting fasteners which are used to attach the spinner to the fan hub.
A further flange may extend from the bracket and is arranged to engage the fairing to provide axial retention of the fairing.
Preferably anti-rotation features are provided to prevent rotation of the brackets. Such features may comprise dowels which engage the brackets.